Fluidized bed reactor utilizing zonal fluidization and anti-mounding air distributors

ABSTRACT

A fluidized bed reactor in which a grate is disposed in a housing for receiving a single bed of particulate material. The interior of the housing below the grate is divided into a plurality of zones and air is selectively passed through portions of the grate to fluidize corresponding portions of the bed above the zones. A plurality of air distributors are provided in the bed for reducing the height of the particulate material accumulating in various portions of the bed.

BACKGROUND OF THE INVENTION

This invention relates to a fluidized bed reactor and, moreparticularly, to such a reactor in which heat is generated by thecombustion of particulate fuel in a fluidized bed.

Fluidized bed reactors, usually in the form of combustors, boilers,gasifiers, or steam generators, are well known. In a normal fluidizedbed arrangement, air is passed through a perforated plate, or grate,which supports a bed of particulate material, usually including amixture of fuel material, such as high sulfur bituminous coal, and anadsorbent material for the sulfur released as a result of the combustionof the coal. As a result of the air passing through the bed, the bedbehaves like a boiling liquid which promotes the combustion of the fuel.In addition to enjoying a high capability for reducing the amount ofsulfur in the gases introduced to the atmosphere, such an arrangementpermits relatively high heat transfer rates per unit size, substantiallyuniform bed temperatures, relatively low combustion temperatures, andreduction in corrosion and boiler fouling.

In the fluidized bed combustion process, the coal and adsorbent arecontinuously introduced into the bed by suitable feeders, injectors, orthe like and the spent coal and adsorbent are discharged from the lowerportion of the bed, usually through a gravity drain pipe extendingthrough a wall of the heat exchanger or through a discharge opening.

In order to optimize operating conditions, the fluidized bed has oftenbeen divided into a plurality of zones, usually by selectivelyintroducing the fluidizing air into certain portions of the bed atdifferent times. This enables selected zones to be fluidized whileothers are dormant to accommodate changing load or start-up conditions.

For example, this selective, or zonal, fluidization simplifies start-upsince only a discrete zone of the bed need be preheated to supportignition, which will then readily proprogate to adjacent zones as theyare brought into service. Also, load control may also be easily achievedby zonal fluidization by increasing or decreasing the number of zoneswhich are fluidized. Further, zonal fluidization enables hot gases toback flow from operating zones through the dormant beds for bedtemperature maintenance prior to rapid light-off and ignition ofadjacent bed sections.

However, when zonal fluidization is utilized, the area of the bed whichis fluidized tends to expand in height above the grid. As a result, theflow of air and the gaseous products of combustion through the fluidizedbed causes the particulate materials to tend to build up, or mound, onthe unfluidized portion of the bed. This mounding, of course, destroysthe parameters under which the bed operates, and can severely effect itsefficiency.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide afluidized bed reactor which utilizes zonal fluidization and yeteliminates any disadvantages normally associated with this technique.

It is a further object of the present invention to provide a fluidizedbed reactor of the above type in which mounding of the particulatematerial on any portion of the bed is eliminated.

It is a further object of the present invention to provide a fluidizedbed reactor of the above type in which discharge nozzles are providedfor discharging a stream of air into the bed for eliminating anymounding of particulate material in the bed.

Toward the fulfillment of these and other objects, the reactor of thepresent invention includes a grate supported in a housing and adapted toreceive a bed of particulate material. A source of air is selectivelypassed through selected portions of the grate to fluidize thecorresponding portions of the bed of particulate material. A pluralityof nozzles are disposed in the housing for reducing the build-up of theparticulate material in one or more of the bed portions.

BRIEF DESCRIPTION OF THE DRAWINGS

The above brief description, as well as further objects, features andadvantages of the present invention will be more fully appreciated byreference to the following detailed description of the presentlypreferred but nonetheless illustrative embodiment in accordance with thepresent invention when taken in conjunction with the accompanyingdrawings in which:

FIG. 1 is a vertical sectional view of a portion of a reactor accordingto the present invention; and

FIG. 2 is a view similar to FIG. 1, but depicting an alternateembodiment of the reactor of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 of the drawings, the reference numeral 10 refers ingeneral to an enclosure forming a major portion of a fluidized bedreactor which may be in the form of a boiler, a combustor, a steamgenerator or any similar type device. The enclosure 10 consists of afront wall 12, a rear wall 14, and two sidewalls, one of which is shownby the reference numeral 16. According to the exemplary embodimentshown, each wall is formed by a plurality of vertically-extending tubes18 disposed in a spaced, parallel relationship and connected together bya plurality of elongated fins 20 extending for the entire lengths of thetubes and connected to diametrically opposed surfaces of the tubes in aconventional manner. The upper portion of the enclosure 10 is not shownfor the convenience of presentation, it being understood that itconsists of a convection section, a roof and an outlet for allowing thecombustion gases to discharge, also in a conventional manner.

A bed of particulate material, shown in general by the reference numeral22, is disposed within the enclosure 10 and rests on a perforated plate,or grate, 24 extending horizontally in the lower portion of theenclosure. The bed 22 can consist of a mixture of discrete particles offuel material such as bituminous coal, and an adsorbent, such aslimestone, for adsorbing the sulfur released by the combustion of thefuel material.

An air plenum 26 is provided immediately below the plate 24 and isdivided by a pair of vertical partitions into three plenum chambers 26a,26b and 26c. An air conduit 28 is connected to a source of pressurizedair (not shown) and has three vertically extending branch conduits 28a,28b and 28c which extend into the chambers 26a, 26b and 26c,respectively, for introducing the air into the chambers.

A flow control valve 30 is mounted in each branch conduit 28a, 28b and28c and functions to control the flow of air into the chambers 26a, 26b,and 26c, respectively. The air entering each chamber 26a, 26b and 26cpasses through the perforations in the grate 24 and into thecorresponding portions of the bed 22 extending immediately above thechambers for fluidizing the respective bed portions. Thus, selectivezonal fluidization of the respective areas of the bed 22 extending abovethe chambers 26a, 26b and 26c can be achieved by control of the airentering the chambers, for the reasons set forth above.

Three overbed feeders 34 extend through a side wall 16 and receiveparticulate coal from inlet ducts or the like (not shown), and areadapted to feed the coal particles onto the upper surface of the bed 22.The feeders 34 are aligned with the chambers 26a, 26b and 26c,respectively, and can operate by gravity discharge or can be in the formof spreader-type feeders or any other similar device. It is understoodthat additional feeders can also be provided on one or more of the otherwalls forming the enclosure 10 and that additional feeders can beprovided for discharging a particulate adsorbent onto the bed 22.

A drain pipe 36 extends through the wall 14 and has an inlet end portionthat registers with the interior of the enclosure 10 in communicationwith the lower portion of the bed 22. The pipe 36 is thus adapted toreceive the spent bed material as it migrates downwardly in the bed andfunctions to discharge the material from the enclosure 10 by gravity toa screw cooler, conveyor belt, or the like (not shown).

A plurality of air distributors 40 extend through corresponding openingsin the plate 24, and each connects to an air conduit 42. Eachdistributor 40 is formed by a vertically disposed tubular member 40awhich extends through the plenum 26 and the plate 24 and into the bed22, and a horizontal tubular member 40b which is connected to thevertical portion and which discharges the air from its free end portionin a plane above the plane of the plate 24. A conduit 44 is providedwhich connects each distributor 40 to a plurality of additionaldistributors (not shown) to form two rows of distributors respectivelydisposed in the chambers 26a and 26b. A damper 45 is provided in thevertical tubular portion of each distributor for controlling the airflow through the distributors 40.

As a result of the foregoing, air can be selectively discharged from thedistributors 40 to prevent the build-up, or mounding, of particulatematerial in one or more portions of the bed 22 as needed. For example,assuming that, for the purpose of start-up, the valve 30 associated withthe branch conduit 28c was opened and the valves 30 associated with theconduits 28a and 28b were closed, only that portion of the bed 22extending above the chamber 26c would be fluidized. A bed light-offburner (not shown) would be provided through the rear wall 14 immedatelyabove the plate 24 for initially lighting off the bed portion extendingabove the chamber 26c and additional particulate material would beselectively introduced to the bed portion from the corresponding feeder34. The air passing through the portion of the bed 22 immediately abovethe chamber 26c would tend to blow a portion of the particulate materialin a direction from right-to-left as viewed in the drawing, over ontothe other portions of the bed to cause a build-up of the material, asshown by the dashed line. When a predetermined build-up of materialoccurs, air from the conduit 42 is passed through both rows ofdistributors 40 and into the bed portions immediately above the chambers26a and 26b to blow the accumulated particulate material in a directionfrom left-to-right back towards the fluidized portion of the bedextending above the chamber 26c. As a result the height of the entirebed is maintained substantially level as shown by the solid line in thedrawing.

A pair of horizontal headers 48 are connected in fluid communicationwith the tubes 18 forming the front wall 12 and the rear wall 14,respectively, and another pair of horizontal headers 50 are connected influid communication with the tubes 18 forming the sidewalls 16. It isunderstood that headers similar to the headers 48 and 50 are provided incommunication with the upper ends of the walls 12, 14 and 16. As aresult, a fluid to be heated can be sequentially or simultaneouslypassed through the walls 12, 14 and 16 to pick up the heat from thefluidized bed in a conventional manner before it is passed to externalapparatus for further processing.

The embodiment of FIG. 2 is similar to that of the embodiment of FIG. 1and identical components have been given the same reference numerals.According to the embodiment of FIG. 2, the air plenum 26 is divided intoa plurality of chambers 26a, 26b and 26c by a pair of pivotal dampers 60and 62 mounted in the plenum 26 in the spaced relationship shown. Airfrom a conduit 64 is introduced into the chamber 26c and, as is apparentfrom the drawings, the position of the damper 62 will control the flowof air into the chamber 26b, and the position of the damper 60 willcontrol the flow of air into the chamber 26a, to permit selective zonalfluidization of bed portions extending above the chambers 26a, 26b and26c.

Two rows of air distributors 66 are provided which extend through thechambers 26a and 26b, respectively, and are connected to a conduit 68which, in turn, is connected to a source of pressurized air (not shown).The upper end portions of the distributors 66 extend into the bed 22 andhave a discharge head 70 disposed on their upper end portions which headhas one or more discharge openings for discharging the air 68 into thebed 22 in a direction from left-to-right as viewed in the drawings.Therefore, the air distributors 66 operate in the same manner as thedistributors 40 in the previous embodiment to maintain a substantiallyconstant level of particulate material in the bed 22 as shown by thesolid line, and prevent the build-up or mounding of the particulatematerial, as shown for example by the dashed line which could occurduring the zonal fluidization techniques discussed above.

It is understood that openings can be provided on all four faces of thedischarge heads 70 and that by selective control of the air flow throughthe distributors 66 by the dampers 45, the anti-mounding air flow fromthe distributors can be in any horizontal direction desired, includingboth directions perpendicular to the plane of the drawing, depending onthe particular order in which zonal fluidization occurs.

It is further understood that variations in the above arrangements canbe made without departing from the scope of the invention. For example,the air distributors 40 of the embodiment of FIG. 1 can be used in theembodiment of FIG. 2 and vice versa, and the distributors can take adifferent configuration from those discussed above. Also the number andspecific locations of the distributors as well as the zonal fluidizationtechniques can be varied as long as the above objectives and results areachieved. Further a bank, or series, of heat exchange tubes can beprovided in the enclosure 10 for circulating water in a heat exchangerelationship with the bed 22 in a conventional manner.

A latitude of modification, change and substitution is intended in theforegoing disclosure and in some instances some features of theinvention will be employed without a corresponding use of otherfeatures. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the spirit and scopeof the invention therein.

What is claimed is:
 1. A fluidized bed reactor comprising a housing,grate means supported in said housing, a bed of combustible particulatematerial supported on said grate means, means extending in said housingfor supplying additional combustible particulate material to said bed ofparticulate material, an air plenum extending immediately below saidgrate means, said plenum being divided into a first chamber and at leasttwo additional chambers, means for selectively passing air from saidchambers through corresponding portions of said grate means and intocorresponding portions of said bed extending above said chambers toselectively fluidize said bed portions, and an air distributor extendingin each of the bed portions extending above said two additional chambersand directed towards the bed portion extending above said first chamberfor selectively reducing the build-up of particulate material in the bedportions extending above said two additional chambers.
 2. The reactor ofclaim 1 wherein each air distributor comprises a vertical conduitextending through its corresponding chamber, said grate means and intoits corresponding bed portion, and means for supplying air to saidconduit.
 3. The reactor of claim 2 wherein each air distributor includesa discharge member attached to said conduit and adapted to dischargesaid air in a generally horizontal direction above the plane of saidgrate means.